Separation of oxygenated compounds



Patented Nov. 3, 195$ UNITED STATES PATENT OFFICE SEPARATION OF OXYGENATED COMPOUNDS ware No Drawing. Application July 18, 1949, Serial No. 105,455

Claims priority, application Netherlands July 26, 1948 12 Claims.

This invention relates to a process for separating various components of a mixture of various oxygen-containing compounds, and particularly such mixtures as are derived from hydrocarbons or are associated with synthetic hydrocarbons as a result of such synthesis. More particularly, the invention is concerned with the separation of mixtures of various oxygenated compounds one from another and from associated hydrocarbons, wherein the oxygenated compounds are normally insoluble or practically insoluble in water under atmospheric conditions of temperature and pressure. The invention is directed especially to the separation of mixtures of oxygenated compounds such as are formed, for example, in the manufacture of synthetic hydrocarbons, as in the Fischer-Tropsch process, in which carbon monoxide and hydrogen are used as initial materials. Such mixtures are also formed, for example, in the so-called x0 process, in which a mixture of carbon monoxide and hydrogen is caused to react with olefins, including mixtures thereof, to form mixtures of aldehydes and alcohols and hydrocarbons.

In these syntheses oxygen-containing compounds of a more or less pronounced polar character, such as acids, esters, ketones, aldehydes, alcohols and ethers, are formed as by-products in addition to the desired hydrocarbons. The compounds of a more pronounced polar character generally have a higher degree of oxidation than the less polar ones. In so far as these oxygen compounds are soluble in water, such as the lower molecular weight ones, they are very easily extractable by means of water and can be separated from the other reaction products, which latter consist of a mixture of hydrocarbons and higher oxygen compounds which are insoluble or practically insoluble in water. Reference may be made to U. S. Patent 2,457,257 for detailed information concerning products produced by the Fischer-Tropsch process.

Such mixtures of oxygen-containing compounds can also be formed in the so-called Oxo process, in which, starting from carbon monoxide, hydrogen and olefins, including mixtures of olefins, oxygen-containing compounds are prepared synthetically.

A principal object of the present invention is to provide a simple and economical method of separating a mixture of the water-insoluble oxygen-containing compounds referred to hereinbefore into fractions, one of which contains compounds of a more pronounced and the other compounds of a less pronounced polar character.

Such a process is very important, since these oxygen compounds represent valuable products. Another object of the invention is to provide an effective and economical process whereby waterinsoluble oxygen-containing compounds referred to hereinbefore are separated from hydrocarbons with which they are associated resulting from the method of synthesis and the oxygenated compounds themselves are separated into fractions of more and less pronounced polar characters.

Now, according to the present invention, a mixture of the said oxygen-containing compounds is separated into a fraction containing compounds of a more pronounced polar character and a fraction containing compounds of a less pronounced polar character by subjecting such mixture to the action of two solvents passed in countercurrent to each other, the one solvent consisting wholly or partially of substances with two or more polar groups or with one polar group and a highly polarizable radical, the other solvent consisting entirely or substantially of one or more paraffinic hydrocarbons, preferably with a boiling range outside the boiling limits of the initial mixture.

It is recommendable that only fractions with a relatively narrow boiling range (for example from 10 to 40 C.), which by ordinary distillation cannot be separated into a fraction containing compounds of a more pronounced polar character and a fraction containing compounds of a less pronounced polar character, should be subjected to the extraction process according to the invention.

The ratio of the distribution coefficients of the compounds to be separated with respect to the solvents is not only dependent on their polarity and chemical properties, but also on the size of the molecules, and this accounts for the fact that when starting from fractions with long boiling ranges the separation will generally be incomplete.

When starting, for example, from a mixture of alcohols and ketones with a long boiling range, the conditions under which the extrac tion takes place can be selected in such a way that in one phase only the alcohols with a low molecular Weight are taken up, while all the ketones and the remainder of the alcohols are found in the other phase; the conditions can also be selected in such a way that in one phase only some of the ketones, namely those with high molecular weights, are taken up and in the other phase the remainder of the ketones and all the alcohols are collected. It will be clear from the abovev that, between these two extremes, all kinds of intermediate cases can be brought about. Generally it will not be possible, therefore, to effect a complete separation between alcohols and ketones in a single operation if the alcohols and ketones present in the mixture being treated extend over a considerable range of molecular weights. 7

Consequently, if it is desired to-separate. mixtures with long boiling ranges by the extraction process of the invention, it is preferable first to separate these mixtures into narrow fractions by ordinary distillation. This distillation fractionation may be made either prior to or after separation of the oxygen-containing compoundsv from the hydrocarbons with which they may be associated as a result of the synthesis process by which the oxygenated compounds are produced.

It is also contemplated according to the invention to separate or extract the oxygen-containing compounds from the hydrocarbons with which they are associated resulting from the method of synthesis with an extracting agent (solvent) which has a higher boiling point than the mixture of oxygenated compounds and hydrocarbons and which consists, either entirely or for the greater part, of substances with two or more polar groups or with a polar group and a highly polarizable remainder. Thus, the same extracting polar solvent may be utilized for both of the extracting separations, the conditions of relative proportions of solvent and mixture to be separated, temperature of operation, and the like being selected depending on the particular mixture being separated, the range of molecular sizes of materials present in the mixture, and the like.

In the extraction of the oxygenated compounds from the associated hydrocarbons by the use of the extracting agents of the invention, the extract phase obtained is preferably washed with a second solvent that is miscible with this phase to a limited extent only, preferentially dissolves the hydrocarbons and has aboiling point beyond the boiling range of the mixture to be separated. Low-boiling hydrocarbons such as butane, pentane and the like, applied as preferential solvent for the hydrocarbons contained in the mixture of oxygenated compounds and associated hydrocarbons may sometimes have the advantage that only relatively small quantities of solvent instead of relatively large quantities of hydro-- carbons present in the initialmixturehave tobe removed from the resultant raffinate (hydrocarbon) phase by means of distillation. Hydrocarbons dissolved in the extract phase of oxygenated compounds may also be removed therefrom in. a washing zone by subjecting said phase, either over the entire washing zone or part thereof, to a temperature gradient, whichshould preferably be gradual.

Since the oxygen compounds tobe separated are insoluble or practically insoluble in: water; the mixtures of these compounds will mainly comprise substances with more than five carbon atoms and will usually have an initial boiling point higher than approximately 110 C. The best results are obtained withmixtures with boiling points not higher than approximately 250? C.

Hydroxy compounds, with or without ether groups, are preferably used as polar extraction agents in the present invention. Excellent results are obtainable with glycols or glycol ethers. Examples of suitable extraction agents with two or more polar groups are: poly-alcohols, butylene glycols, hexylene glycols, poly-alcohol ethers such as. polyethylene glycols. (.diethylene glycol, triethylene glycol, diprcplene glycol, di-trimethylene glycol, and the like), phenyl ethers of glycol, glycerine dimethyl ether, furfural, alkanol amines, oxy-nitro compounds, such as ortho-nitrophenol, and chlorohydrins.

Examples of extraction agents with a polar group and a highly polarizable radical are: nitrobenzene, phenol, cresols, phenyl glycidyl ether, sulfolenes and substituted sulfolenes, sulfolanes and substituted sulfolanes, etc.

The boiling range of the polar solvent need not be entirel'y-outsidethat of the mixture to be separated. If the boiling ranges overlap wholly or partially thev solvent can be recovered by extraction with water, since the polar solvent is usually water-soluble, whereas the compounds to be separated are insoluble or practically insoluble in water.

If the boiling ranges of the solvent and the mixture to be separated do not overlap and the solvent is recovered by distillation, which will generally be the case, solvents with boiling points higher than those of the compounds to be separated are preferable, since the extraction according to the invention is as a rule carried outwith an excess of solvents, so that in the case of a solvent with a high boiling point only the relatively small quantity of oxygen-containing compounds need be evaporated.

Besides pure parafilnic hydrocarbons, such as those which are normally associated with. the oxygenated compounds as formed, for example, in the Fischer-Tropsch' process, petroleum fractions containing no or practically no aromatics,

for example petroleum naphtha fractions poorin aromatics, can also be used as solvent. consisting of one or more paraflinic hydrocarbons.

Paraifinic hydrocarbons are insoluble in water and consequently cannot be separated from the water-insoluble oxygen-containing compounds by extraction with water. The recovery of the second solvent fromthe less polar fraction of oxygenated compounds must, therefore, be effected by distillation, so that the boiling range of this solvent should be, either above or below that of the mixture to be separated.

Since, as a rule, an. excess isapplied also in the case of the second solvent, itwill be preferable to use a hydrocarbon fraction therefor. which is.

poor in or free from aromatics, the boiling range of which is higher than: that of the mixtureto be separated, such as liquid paraffin oil.

The extraction is, as a, rule, carried out attemperatures of from 0 to C. The solvents used must be selected in: such a way that two liquid phases are formed.

Accordingly, as the polar characterrof one solvent increases, the dissolving power oft-he; oxygen-containing compounds therein decreases, which should beborne in mind when: selecting this solvent. It may sometimes be preferable to use a mixture of solvents.

To the solvent with the polar groups and/or.

polarizable radical a substance may. be added which more or less modifies thecharacter of the solvent including both the dissolving power and the selectivity; Such a substance is, for example, water; by adding water the total dis-- solving power of the solvent for the oxygenated compounds decreases, which causes. the selectivity of the'solvent mixture to increase.

Various techniques well known in the extrac-- tion art, such as the employment of a tempera.-

ture gradient throughout a part or all of the extraction zone, the use of backwash at either or both ends of the extraction zone, and the like, may be advantageously employed in the practice of the invention.

The invention will be further illustrated by the following examples:

Example I A mixture of C6 and C7 olefins was reacted with a mixture of carbon monoxide and hydrogen by the so-called Oxo process and a product was obtained consisting of oxygen compounds and hydrocarbons. A fraction comprising alcohols and aldehydes, with a boiling range of 140-160 C., was separated from the reaction product by distillation. This fraction, which upon analysis was found to contain 60% by weight of alcohols and 40% by weight of aldehydes was subsequently separated into two fractions in an apparatus comprising seven extraction stages by bilateral counter-current extraction using diethylene glycol and an aromatic-free gasoline hydrocarbon fraction, with a boiling range of 90-110 C., as solvents.

The mixture of alcohols and aldehydes was introduced at the third stage, the diethylene glycol at the first stage and the gasoline fraction at the 7th stage. Seven parts by volume of diethylene glycol and 12 parts by volume of gasoline were employed for each one part by volume of the alcohols-aldehydes fraction. The product obtained from the separated gasoline phase was completely free from alcohols; the product from the diethylene glycol phase was found to consist of 96.2% by Weight of alcohols and 3.8% by weight of aldehydes.

Example II A mixture containing n-butanol-l (boiling point 118 C.) and methyl isobutyl ketone (boiling point 116 C.) in a volume ratio of 50:50, as may be obtained as a very narrow boiling range cut of product produced from a mixture of C4 and C olefins by reaction with carbon monoxide and hydrogen by the so-called Oxo process, was subjected to fractionation by the same method used in Example I, except for each part by volume of mixture fed to the extractor, 1.6 parts by volume of diethylene glycol and 6.4 parts by volume of liquid paraffin oil were employed. The product recovered from the separated diethylene glycol phase was 98.5% of butanol and contained only 1.5% of methyl isobutyl ketone. The product separated from the liquid parafiin phase was 98.5% methyl isobutyl ketone and only 1.5% of butanol.

Example III A mixture of 50% by volume of 2-methylhexanol-l (boiling point 167 C.) and 50% by volume of diisobutyl ketone .(boiling point 169 C.) was fed to the middle stage of an 11-stage extraction column. For each two parts by volume of said mixture, 11.3 parts by volume of diethylene glycol were fed to the first stage of the extraction apparatus and 8.7 parts by volume of liquid paraffin were fed to the 11th stage. The solvents were passed through the column in countercurrent. The product recovered from the separated diethylene glycol phase was 98.7% alcohol and contained only 1.3% of diiso-butyl ketone. The product recovered from the liquid paraffin phase was 98.7% of diisobutyl ketone and only 1.3% of 2-methylhexanol-1.

6. Example IV When the reaction product obtained in the hydrogenation of carbon monoxide by the socalled catalytic Fischer-Tropsch process is cooled and intimately contacted with an aqueous alkaline solution, two liquid phases are obtained, one of the aqueous phase containing the lower molecular weight water-soluble oxygenated organic compounds comprising aldehydes, ketones, alcohols, acids and esters (depending on the conditions, the esters may be completely saponiiied), and the other an oil phase comprising hydrocarbons and hydrocarbon-soluble,

water-insoluble, oxygenated organic compounds.

When the oil phase is separated by distillation into relatively narrow boiling range fractions (say, 40 C. to 50 C. range) to produce fractions normally containing in the order of by volume of hydrocarbons and 20% by volume of oxygenated organic compounds, the oxygenated compounds are separable from the hydrocarbons by countercurrent contacting extraction at, for example, 20 -C., with highly polar solvents such as diethylene glycol, sulfolane, monoethanol amine, and the like. For example, when such a, fraction having a boilin range of -167 C. and comprising paraflinic hydrocarbons, ketones and alcohols in the proportions of about 821:1, respectively, is countercurrently contacted in a three-step extraction system at 20 C., for each 10 parts by volume of the mixture supplied to the middle step or stage, with four parts by volume of diethylene glycol supplied to the first step, and 0.3 part by volume of water injected into the third step as washing agent, the extract obtained from the separated diethylene glycol phase contains paraffinic hydrocarbons, ketone and alcohol in the approximate volume proportions of 8:44:48, respectively.

When the separated mixture of oxygenated compounds, comprising the ketones and alcohols, is subjected to fractionation by extraction with two countercurrently flowing streams of a solvent pair of the invention, for example, sulfolane-paramn hydrocarbons, or the separated diethylene glycol phase containing the ketones and alcohols, without separation of the glycol solvent from the other substances, is countercurrently contacted with a suitable parafiin hydrocarbon solvent, such as a gas oil fraction, according to the methods of Examples I-III, the oxygenated compounds are readily fractionated, with the separated polar solvent phase being enriched with respect to the alcohols and the separated hydrocarbon phase being enriched with respect to the ketones. The degree of separation is controlled by selection of solvent ratios, one to the other, and to the mixture of oxygenated compounds being separated, the range of molecular weights of the oxygenated compounds present as may be controlled by distillation fractionation, the particular solvent pair employed, and the like, as will be readily understood from the foregoing description of the invention.

The invention claimed is:

1. A process for separating a mixture of hydrocarbon-soluble, water-insoluble aliphatic alcohols and aliphatic carbonylic compounds selected from the group consisting of aldehydes and ketones having a boiling range of not more than about 40 C. and a boiling point not higher than about 250 0., and being essentially free from hydrocarbons of the same boiling range,

acumen into one fraction enriched in. alcohols and another fraction enriched in said carbonylic compounds, which process comprises subjecting said mixture to solvent extraction with two substantially mutually immiscible solvents flowing. in. countercurrent to each other, wherein one solvent consists essentially of an organic polar liq-- 3. A. process according to claim 1. wherein the.

polar solvent is an organic hydroxy'compound.

4. A process according, to, claim; lwherein the. polar solvent is a glycol.

5. A process according to:claim 1, wherein the hydrocarbon solvent is a paraflin oil. having: a. boiling range above the boiling range of. the mixture to be separated.

6.. A process according to. claim 1, wherein the. polar solvent is diethyleneglycol and thehydrocarbon solvent is a paraffin oil having a boiling range above the boiling range ofthe-mixture-to be separated.

7. A process according to claim 1, wherein the mixture of alcohols and carbonylic compoundsto be separated is derived from an Oxo product and. has a boiling range of about 1409-160" C;,,-

line hydrocarbon fraction having aboiling range.-

of about 90-110 C.

8. A process for separating a mixture: of hy-- drocarbon-soluble, water-insoluble; aliphatic 2'17 cohols and aliphatic ketones having a boilin range of not more than about: 40 C; and:a boil.- ing point of not higher. than about 250 C.,, and being essentially free from hydrocarbons; of. the same boiling range, into one fraction enriched in alcohols and another fraction enriched in said aliphatic ketones, which process comprises subjecting said mixture to solvent extraction with two substantially mutually immiscible solvents flowing in. countercurrent to each other, wherein one solvent consists essentiallyv of aglY- col and the other solvent is essentially a par.-

3o JOAN. HENRI VAN DER WAALS.

References Cited in the file of this patent UNITED STATES PATENTS 35 Number Name Date 2,081,721 Van Dijck et al. May 25, 1937 2,245,945 Van Dijck et al. June 17, 1941 2,274,750 Soenksen et al Mar. 3, 1942 2,418,899 Pevereet a1 Apr. 15, 1947 40 2,470,782 McGrath et a1 May 24, 1949 2,516,940 Arnold et al; Aug. 1, 1950 2,580,750 Fleming Jan. 1, 1952- 2,583-,620 Wrightson' Jan. 29, 1952 5 FOREIGN PATENTS Number Country Date 441,104 Great Britain Jan. 13', 1936 8' amni'c hydrocarbon mixture. with a boiling range outside the boiling limits of saidmixture.

9. The process according to claim 8, wherein said glycol is diethylene glycol;

10. A process according to claim 8; wherein the: mixture of alcohols and ketones ha an average boiling point of about 167-169 C., the glycol solvent is essentially diethylene glycol and the hydrocarbon solvent is liquid paraifin oil having a boiling range above the boiling range ofthe mixture to be separated.

11'. A process for separating a mixture of hydrocarbon-soluble, water-insoluble aliphatic alcohols and. aliphatic aldehydes having a boiling range of not morethan about 40 C. and a boiling point of nothigher than about 250 C., and being essentially free from hydrocarbonsv of the same boiling range, into one fraction enriched in alcohols and another fraction enriched in said aliphatic. aldehydes, which process comprises subjecting, said mixture to solvent extraction with two substantially mutually immiscible solvents flowing in countercurrent to each other, wherein one solvent consists essentially of a glycol and the other solvent is essentially a paraffinic hydrocarbon mixture with a boiling range outside the boiling limits of said mixture.

12. The process according, to claim 11 wherein saidv glycol is diethylene glycol. 

1. A PROCESS FOR SEPARATING A MIXTURE OF HYDROCARBON-SOLUBLE, WATER-INSOLUBLE ALIPHATIC ALCOHOLS AND ALIPHATIC CARBONYLIC COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF ALDEHYDES AND KETONES HAVING A BOILING RANGE OF NOT MORE THAN ABOUT 40* C. AND A BOILING RANGE OF NOT MORE THAN ABOUT 250* C., AND BEING ESSENTIALLY FREE FROM HYDROCARBONS OF THE SAME BOILING RANGE. INTO ONE FRACTION ENRICHED IN ALCOHOLS AND ANOTHER FRACTION ENRICHED IN SAID CARBONYLIC COMPOUNDS, WHICH PROCESS COMPRISES SUBJECTING SAID MIXTURE TO SOLVENT EXTRACTION WITH TWO SUBSTANTIALLY MUTUALLY IMMISCIBLE SOLVENTS FLOWING IN COUNTERCURRENT TO EACH OTHER, WHEREIN ONE SOLVENT CONSISTS ESSENTIALLY OF AN ORGANIC POLAR LIQUID WITH TWO POLAR OXYGEN-CONTAINING GROUPS AND THE OTHER SOLVENT, IS ESSENTIALLY A PARAFFINIC HYDROCARBON MIXTURE WITH A BOILING RANGE OUTSIDE THE BOILING LIMITS OF SAID MIXTURE. 